When the system is small and produces a small quantity of letters, the printer is generally not mechanically coupled to the folder-inserter. Transfer is performed manually. The user takes the sheets at the outlet from the printer and inserts them in an inlet of the folder-inserter. Two types of printer need to be distinguished: some printers provide the sheets on which a letter has been printed in an order suitable for enabling the sheets to be inserted directly in an envelope. Other printers provide the sheets in an order that is unsuitable for direct insertion in an envelope since the addressee would find the last page in front of the first page. The user must therefore not only transfer the sheets manually, but must additionally change the order of the sheets.
To make such a system of mail handling more practical, the outlet of the printer could be mechanically coupled to the inlet of the folder-inserter. However, such mechanical coupling must solve the problem of inverting page order if the printer already owned by the user does not provide pages in the proper order for direct insertion in an envelope. A mechanical page inverter could be associated with the printer, such as described in European patent applications EP 0 365 283 and EP 0 398 187, however such mechanical devices are difficult to fit to an already-existing printer that a user does not want to change because of the cost of such a change.